Put the butter and the cream in a pan and put over the heat until the butter has melted and the mixture is bubbling. Remove the pan from the heat and add the milk choclate pieces.Stir until the chocolate has melted.
(If you want to make liquors then now is the time to add 2tbsp of alcohol, something like Grand Marnier would be lovely!!).
Put the bowl into the fridge and leave until it has set and is firm (takes about 3hours).
Once it has firmed up you can get a spoon full of the mixture and roll it into a ball using the palms of your hands. This can get quite messy so it's useful to have a cloth to hand!
Next you need to roll each of the balls in some cocoa powder to give it a light dusting.
Put the truffles back into the fridge to firm up again (if you need to do these quickly you can put them into the freezer for a short time).
Melt the dark chocolate over a pan of simmering water.
You can now dip the truffles into the melted chocolate using a cocktail stick. Let the excess chocolate drip off and then leave to set on a plate or tray covered with baking parchment.
Allow the truffles to set again in the fridge and then using some melted white chocolate and a disposable piping bag, pipe over 3 or 4 lines on each truffle.
If you don't have a piping bag you can drizzle some melted white chocolate over using a spoon.